Various granules containing ascorbic acid or salts thereof are produced by spraying a binder with the materials being fluidized in a fluidized-bed spray granulator, or by addition of a binder solution with the materials to be kneaded in a granulator or kneader, or by other techniques.
However, calcium ascorbate is subject to coloring during the usual procedures such as granulation by addition of a binder solution with the materials being kneaded in a kneader, or by spraying a binder with the material being fluidized in a fluidized-bed spray granulator. It is a problem that the resulting products are yellow while the starting crystalline powders of calcium ascorbate are white.
A method is disclosed in U.S. Pat. No. 2,442,461 to improve the stability of an aqueous solution of calcium ascorbate against its decomposition. This method is to add thioglycolic acid into the calcium ascorbate solution.
To stabilize calcium ascorbate powders, it has been proposed to coat the powders with hydrogenated castor oil etc.
A method is disclosed in FR 1,498,600 to improve the stability of Calcium ascorbate per se against coloring. This method consists of neutralizing the ascorbic acid with calcium carbonate in an aqueous solution containing an organic solvent to obtain white calcium ascorbate.
However, the satisfactory improvement against coloring in the granulation of calcium ascorbate has not yet been reported. And, the prior methods for producing calcium ascorbate are not sufficient to obtain the desirable product.
Thus it has been desired to produce granulation products, which are free from yellowing even in the form of solid preparations, in which calcium ascorbate itself is stable, and which can be combined easily with other ingredients such as other medicines.